The invention relates to a method for manufacturing a pipe part from fibre-reinforced thermosetting synthetic material comprising a main pipe part and at least one branch pipe part connected to it.
The invention also relates to a mandrel for manufacturing such pipe parts.
There are different methods known for manufacturing a pipe part of the above type such as a T-piece, from fibre-reinforced thermosetting material. In known method, synthetic resin impregnated fibres are applied to a steel mandrel defining the inside shape of a T-piece, preferably by winding and after the T-piece has reached the desired shape, the synthetic resin is cured, after which the steel mandrel consisting of several parts is removed from the T-piece. This method is mainly utilized in the manufacture of T-pieces having relatively small diameters up to about 300 mm. In the manufacture of T-pieces having a greater diameter, This method has the disadvantage that the mandrels are very expensive and that they are also extremely unwieldy. Furthermore, the time necessary for applying the resin impregnated fibres on the mandrel takes so long, that the resin applied first will cure prematurely, so that the manufacture of a T-piece of such dimensions would have to be carried out in several successive stages.
It is for this reason that in the production of large diameter T-pieces, a method is mostly utilized wherein a V-shaped opening is made in the wall of the main pipe part, into which a complementary V-shaped extremity of a branch pipe part is inserted. The space between the two pipe parts is then filled with a filling resin. In the area of the junction of the two pipe parts, resin impregnated fibres are wound around the T-pieces so formed, until a thickness has been reached corresponding to the required strength of the T-piece, after which it is cured. This method has a number of disadvantages. It is fairly difficult to achieve a precise fit between the two pipe parts, as both the V-shaped opening in the main pipe part and the V-shaped extremity in a branch pipe part have to be made by sawing. That is the reason why a filling resin is mostly used when assembling both pipe parts into a T-piece. Furthermore, with this method it is not possible to achieve a smooth transition between the main and the branch pipe parts. In the case of extremely large T-pieces, where the T-piece is internally accessible for a person, this transition may be improved subsequently, but in the case of T-pieces with a diameter of about 500 mm., this is impossible.
Finally, T-pieces manufactured in this way may only be loaded upto a limited internal pressure, which is too low for pipe systems intended for high pressure applications.